Clouds are classified into a system that uses Latin words to
describe the appearance of clouds as seen by an observer on the ground.
The table below summarizes the four principal components of this
classification system (Ahrens, 1994).

Latin Root

Translation

Example

cumulus
stratuscirrusnimbus

heap
layercurl of hairrain

fair weather cumulus
altostratuscirruscumulonimbus

Further classification identifies clouds by height of cloud base.
For example, cloud
names containing the prefix "cirr-", as in cirrus clouds, are located at
high levels while cloud names with the prefix "alto-", as in
altostratus, are found at middle levels.
This module introduces several cloud groups. The first three groups are
identified based upon their height above the ground. The fourth group consists
of vertically developed clouds, while the final group consists of a
collection of miscellaneous cloud types.

High-Level CloudsHigh-level clouds form above 20,000 feet (6,000 meters) and since the
temperatures are so cold at such high elevations, these clouds are
primarily composed of ice crystals.
High-level clouds are typically
thin and white in appearance,
but can appear in a magnificent array of colors
when the sun is low on the horizon.

Mid-Level CloudsThe bases of
mid-level clouds typically appear between 6,500 to 20,000 feet
(2,000 to 6,000 meters). Because of their
lower altitudes, they are composed primarily of water droplets,
however, they can also be composed of ice crystals
when temperatures are cold
enough.

Low-level CloudsLow clouds are of mostly composed of water droplets since their bases
generally lie below 6,500 feet
(2,000 meters). However, when temperatures are
cold enough, these clouds may also contain
ice particles and snow.